The present invention relates to an objective lens for use with high-density information storage disks.
Optical pickup devices such as video disk devices utilizing laser beams are widely known in the art. A laser beam emitted from a laser beam source is focused by an objective lens onto the surface of a disk to be reproduced, and the laser beam as reflected from the disk surface passes again through the objective lens back toward the laser beam source. The information recorded on the disk can be detected by the intensity of the laser beam as received. The objective lens is rendered movable for tracking and focusing purposes, and hence is required to be small in size and light in weight. It is necessary that the spacing or operating distance between the objective lens and the disk surface be as large as possible since the objective lens would tend to hit the disk surface unless the distance therebetween were greater than a certain interval. To read the information recorded at a high density on the disk, the objective lens needs to have a resolving power of about 1 micron. The objective lens is therefore required to have a numerical aperture (N.A.) of about 0.5.